The invention relates to a clutch actuator with automatic wear compensation for the preferential actuation of a starting clutch for vehicles that is closed in the unactuated state.
A clutch for a vehicle serves to completely separate the non-positive connection between the motor and the transmission during shifting operations of the transmission and gradually build up the same when starting. Said clutch contains a clutch disk assigned to the motor and a clutch disk assigned to the transmission. Both clutch disks are provided with friction linings and, in the closed state of the clutch, are pressed against one another by a clutch reaction force, which is generally provided by a spring.
A clutch actuator transmits a disengaging force that is opposed to the clutch reaction force to the clutch. As a result, the clutch disks can be separated from one another so that the non-positive connection between motor and transmission is interrupted. However, for starting, the clutch can also be transferred to a state of slipping, in which the clutch disks rub against one another and only a freely selectable part of the torque provided by the motor is transmitted to the transmission. Through the rubbing, the friction linings wear and become thinner over time so that the kinematic deflection condition between the clutch actuator and the clutch changes. For this reason, the clutch actuator has to be continuously readjusted by way of a length compensation so that upon actuation of the clutch it transmits the disengaging force to the clutch without play. Here said adjustment must be mechanically stable enough that it is not changed by the action of the disengaging force.
WO 2012 119 612 A1 discloses a clutch actuator, in which an actuator piston is subjected to the disengaging force by an auxiliary energy source and transmits this disengaging force to the clutch via a piston rod. For the length compensation, the piston rod, which has an external transmission thread, is coupled to the actuator piston via an intermediate piece with an internal transmission thread corresponding thereto. The total length of piston length and intermediate piece is automatically readjusted by virtue of the fact that, in the closed state of the clutch, the non-rotatingly mounted piston rod is screwed, by the clutch reaction force, into the intermediate piece, wherein the intermediate piece is inevitably rotated. The actuator piston has a blocking region, which, on actuating the clutch, enters into a frictional connection with a region on the intermediate piece corresponding thereto and blocks the rotary movement of the intermediate piece. By way of the intermeshing transmission threads and the anti-rotation feature of the piston rod, a relative movement between piston rod and intermediate piece is thus blocked.
The object of the present invention is to further develop the clutch actuator according to the prior art so that it can be produced in a simpler manner and with fewer components.
This and other objects are solved by a clutch actuator according to embodiments of the invention.
Within the scope of the invention, a clutch actuator for transmitting a disengaging force FA to a disengaging device of a clutch has been developed. This clutch actuator comprises an actuating element that can be subjected to the disengaging force FA and a piston rod for transmitting the disengaging force FA from the actuating element to the disengaging device. Here, the piston rod is mounted against a connecting region of the actuating element so that the piston rod can be moved against the connecting region through the clutch reaction force FK of the clutch. The positioning of connecting region and piston rod relative to one another brought about by such a movement can be fixed by subjecting the actuating element to the disengaging force FA.
According to the invention, the actuating element is designed for the at least partial deflection of the disengaging force FA into a normal force FN and/or radial force FR that is active between the connecting region and the piston rod. This normal force FN and/or radial force FR fixes the positioning of connecting region (14, 24) and piston rod (15, 25) relative to one another.
It has been recognized that the intermediate piece provided according to the prior art can be saved in this manner. Furthermore, a separate blocking region on the actuating element is no longer required. Instead, the additional normal force FN and/or radial force FR is introduced, for the purpose of fixing the positioning, exactly at the point at which the piston rod and the connecting region are in contact for the purpose of guiding the mutual movement anyway.
This type of fixing has the advantage, furthermore, that it is immediately effective when the actuating element is subjected to the disengaging force. The blocking according to the prior art was activated by virtue of the fact that the actuator piston was moved into a position in which its blocking region entered into the frictional connection with the region on the intermediate piece corresponding thereto. At least for a brief moment, the blocking was thus not initially effective with every actuation of the clutch, while the actuator piston covered the idle travel up to the establishment of the frictional connection on the blocking region. In the event of a sudden powerful actuation, the piston rod and the intermediate piece could thus be unintentionally moved against one another and the automatic adjustment in this regard could be worsened. The disengaging force FA necessary for opening the clutch is very large and can typically be above 6,000 N.
Furthermore, in contrast with the prior art, threads on the piston rod and on the connecting region can also be omitted. In a particularly advantageous configuration of the invention, an outer circumference of the piston rod is slideable against an inner circumference of the connecting region. The outer circumference of the piston rod and the inner circumference of the connecting region need not be specially processed; there can be, in each case, smooth surfaces that slide against one another or slide past one another without touching, for example. The clutch rod and the connecting region are thus easier to produce and less susceptible to wear.
However, the fixing according to the invention can also be utilized in the configuration in which the piston rod has an external transmission thread, which engages in an internal transmission thread on the connecting region. The mutually engaging transmission threads partly convert the linear movement of the piston rod driven by the clutch reaction force FK to a rotary movement of the piston rod relative to the connecting element. Here, by way of the pitch of the thread, an additional degree of freedom is available. In this configuration, the fixing according to the invention has the advantage that the piston rod need no longer be mounted in a non-rotational manner.
Advantageously, means for exerting a preload force FF, that is effective between the piston rod and the actuating element, said preload force counteracting the clutch reaction force FK of the clutch, are provided. These means can comprise, for example, a preloading spring. The preload force FF is of subordinate importance regarding the length compensation; it can be used to set the contact pressure of the two clutch disks against one another that is considered to be the unactuated state of the clutch for the purpose of the length compensation. The main purpose of the preload force FF, even in the unactuated state of the clutch actuator, is to exert a certain minimum force on the disengaging device and to ensure that no play develops between the piston rod and the disengaging device.
In a particularly advantageous configuration of the invention, the normal force FN or the radial force FR fixes the positioning of connecting region and piston rod relative to one another via a self-amplifying frictional connection. Self-amplification in this connection is to be understood to mean that the magnitude of the normal force FN or of the radial force FR automatically tracks the magnitude of the disengaging force FA. The piston rod and the connecting region are then only subjected to the respectively needed magnitude of normal force FN or radial force FR, which protects the components.
In a particularly advantageous configuration of the invention, the connecting region is mounted on the actuating element so that said connecting region can be radially pivoted in the direction of the piston rod through a linear movement of the actuating element in the axial direction of the piston rod. The normal force FN or radial force FR is then proportional to the disengaging force FA exerted on the actuating element. The proportionality constant is determined by the geometry of the mounting.
Advantageously, the connecting region is designed as a connecting element and/or is part of a connecting element, wherein this connecting element can be fixed against a stop on the actuating element through the clutch reaction force FK and/or through the preload force FF. A separate production of actuating element and connecting element can be simpler than a one-piece production of an actuating element with integrated connecting element. Assembly is also simple. Here, the same effect is ultimately achieved as if actuating element and connecting element were a one-piece unit. This applies, in particular, when the connecting element is fixed by the typically large clutch reaction force FK.
In a further advantageous configuration of the invention, the connecting region is designed as a connecting element, which is pivotably mounted against the actuating element. Here, the connecting element and the actuating element can consist, in particular, of the same material and the connecting element, together with the actuating element, can be realized as a single component. For example, a combination of an actuating element with a connecting element mounted against the same via a fixed-body joint, can be produced in one piece. However, the connecting element can also be a separate component, which is mounted against the actuating element via a hinge or a similar connection. Such connections are more expensive to produce but are more durable than fixed-body joints in which the material is subjected to bending with every positional change.
In a particularly advantageous configuration of the invention, an end stop position is provided, with which the actuating element is in contact when the clutch is engaged. This end stop position is then, on the one hand, a fixed reference point for the length compensation, which takes place through the relative movement between the connecting region and the piston rod. On the other hand, in a further particularly advantageous configuration of the invention, means for reducing and/or eliminating the normal force FN and/or the radial force FR can be provided, said means being actuable by bringing the actuating element into the end stop position. The length compensation through the relative movement between the piston rod and the connecting region, which, in the unactuated state of the clutch, is driven by the clutch reaction force, is then obstructed as little as possible by way of friction between the connecting region and the piston rod. An example for such a means for reducing and/or eliminating the normal force FN and/or the radial force FR is a connecting element that is pivotably mounted on the actuating element, said connecting element forming a contact point of the actuating element to the end stop position when the clutch is engaged.
In a further particularly advantageous configuration of the invention, the actuating element is designed as a piston, which is displaceably mounted in a housing and, in this housing, closes off a pressure chamber. The actuating element can then be subjected to the disengaging force by introducing a pressure medium into the pressure chamber. Especially in the case of utility vehicle clutches, major forces sometimes have to be exerted with the result that the actuation with the foot-exerted force of the driver alone is strenuous over time. However, this foot-exerted force can be amplified many times with simple means by way of pneumatics or hydraulics and subsequently introduced into the pressure chamber by the pressure medium. Furthermore, an electronically controlled clutch (clutch by wire), for example in automated shift transmissions, can also direct the disengaging force to the actuating element by introducing a pressure medium into the pressure chamber.
The invention, and in particular the length compensation, however, functions entirely analogously when another source of force is utilized for subjecting the actuating element to the disengaging force. For example, the actuating element of an electronically controlled clutch (clutch by wire) can also be electromechanically moveable, for example by a motor.
The necessity of a length compensation is more pronounced in utility vehicles than in passenger cars. Since the clutch reaction force FK in the case of a utility vehicle clutch is substantially greater than in the case of a clutch for passenger cars, a plurality of mechanical transmissions are typically arranged in the chain of action between the piston rod and the clutch disks, said mechanical transmissions reducing the necessary disengaging force FA and in turn extend the necessary actuation travel. Thus, a lining wear of the order of magnitude of 5 to 8 mm translates into a necessary length compensation of the order of magnitude of 60 to 65 mm. This length compensation can thus be significantly greater than the actuation travel of the actuating element necessary for the transition from a fully closed to a fully opened clutch, which actuation travel can be of the order of magnitude of 20 to 30 mm, for example.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.